PROJECT SUMMARY/ABSTRACT The circadian clock regulates many aspects of physiology and behavior. These rhythms are coordinated by the master clock in the suprachiasmatic nuclei (SCN) of the hypothalamus. This core clock is composed of a transcriptional/translational negative feedback loop, where transcriptional activators BMAL1/CLOCK regulate the expression of their own repressors, the PER and CRY proteins. This repression step is critical, as without it, there's no rhythm. The key step in the repression process is coordinated translocation of the PER/CRY protein complex from the cytoplasm to the nucleus. Recently, we've found that the same NRON complex that regulates translocation of the NFAT pathway, also regulates the translocation of the PER/CRY complex and circadian clock function. The NFAT pathway regulates development but also innate and adaptive immunity in the periphery and the central nervous system. This NRON complex is comprised of signaling molecules, e.g. CSNK1e, GSK3B, and DYRK1 (known clock kinases), but also scaffolding (IQGAP1, the ncRNA NRON), proteolysis (PSMD11, CUL4B, UREB1), and nuclear translocation (KPNB1, CSE1L, TNPO1). Using genetics in human cells and in Drosophila, we've shown that most of these components alter period length or are required for clock function altogether (KPNB1, PSMD11). Further, pharmacological perturbation of the NFAT pathway alters SCN physiology and circadian function. Here, we seek to better understand this key repression step by understanding its biochemical and cell biological mechanisms, study the cross talk between the two pathways in the SCN, and generate a suite of genetic models to characterize the role of these genes in modulating the SCN clock and the sleep/wake cycle. This work will provide the first broad linkage between NFAT-regulated cell and physiological processes including immunity in the brain and core clock function that governs behavior and associated physiologies.